It is generally believed that antimicrobial peptide has a broad antimicrobial spectrum such that drug resistant bacterium hardly appears, and therefore antimicrobial peptide is expected to be used for the purpose of preventing and treating bacterial infectious diseases in human beings and animals or providing antimicrobial properties to products such as food. A large number of antimicrobial peptides have been isolated from various animals and plants to date.
As examples, antimicrobial peptides disclosed in International Publication No. WO98/51794, International Publication No. WO99/26971, International Publication No. WO00/09553, International Publication No. WO00/59527, International Publication No. WO01/09175, Japanese Laid-Open Patent Publication No. 2000-63400, Japanese Laid-Open Patent Publication No. 2001-186887, and ‘The 67-kDa Laminin Receptor Originated from a Ribosomal Protein that Acquired a Dual Function During Evolution’, Elena Ardini et al., Volume 15, Issue No. 8, 1998, p. 1017-1025, are being identified.
Every antimicrobial peptide disclosed in each aforementioned publication is discovered in and isolated from peptide that originally exists as antimicrobial peptide in nature (or peptide of which a part of the amino acid sequence of an isolated natural antimicrobial peptide is being modified). As long as these peptides that originally exist as antimicrobial peptides are being used as the main component, it is difficult to develop antimicrobial agent having antimicrobial performance that exceeds the antimicrobial activity and the antimicrobial spectrum accomplished by such original peptides in nature.
One of the objects of the present invention is to provide, without utilizing the developmental approach of antimicrobial agent including the conventional antimicrobial peptides, antimicrobial peptides composed of artificially designed amino acid sequences that are different from peptides existing and functioning as antimicrobial peptides in nature, and polynucleotides encoding such peptides. In addition, one of the objects is to provide antimicrobial agents (pharmaceutical compositions) having such antimicrobial peptides as the main component.